A defect has presented in some iPhone 5 touch panels produced by Wintek which may affect the ability to meet initial shipment targets for the launch which is expected in October, according to iPhone supply chain makers.

In response, Wintek simply indicated that all of its products are being delivered on schedule.

The defect, "delayed bubble", is difficult to avoid during panel production, particularly when the defect is not detected during the process of laminating touch panels, and only later found during assembly, the sources said. Since the manufacturing process of touch panels used in iPhone 5 is of the same as that for iPhone 4, Wintek is expected to remedy the defect quickly, the sources indicated.

Wintek accounts for 20-25% of the total production of touch panels used in iPhone 5, while Taiwan-based TPK Holding accounts for 60-65% and Chimei Innolux for the remainder, the sources indicated.

Apple aims to ship 25-26 million units of iPhone 5 in the fourth quarter, the sources claimed.